An aircraft is propelled by one or more turbojet engines each housed in a nacelle that also houses a collection of ancillary actuating devices associated with the operation thereof and performing various functions when the turbojet engine is operating or stationary. These ancillary actuating devices notably comprise a mechanical system for the actuation of the thrust reversers.
A nacelle generally has a tubular structure comprising an air intake forward of the turbojet engine, a middle section intended to surround a fan of the turbojet engine, a rear section which may house thrust reversal means and is intended to surround the combustion chamber of the turbojet engine, and generally ends in a jet pipe, the outlet of which is situated downstream of the turbojet engine.
Modern nacelles are often intended to house a bypass turbojet engine capable, via the blades of the rotating fan, of generating the flow of hot air (also known as the primary flow) from the turbojet engine combustion chamber.
A nacelle generally has an outer structure which, together with a concentric inner structure, defines an annular flow duct, also known as a flow path, intended to channel a flow of cold air, known as the secondary or bypass air, which passes around the outside of the turbojet engine. The primary and secondary flows are ejected from the engine via the rear of the nacelle.
Each airplane propulsion unit is thus formed of a nacelle and of a turbojet engine, and is suspended from a fixed structure of the airplane, for example under a wing or on the fuselage, via a pylon or a strut attached to the engine or the nacelle.
The rear section of the nacelle is usually formed of a first and of a second half-shell of substantially semicylindrical shape, one on each side of a longitudinal vertical plane of symmetry of the nacelle, and mounted such that they can move in such a way that they can be deployed between a work position and a maintenance position with a view to providing access to the engine. The two half-shells are generally pivot-mounted about a longitudinal axis that forms a hinge at the top part (in the 12 o'clock position) of the nacelle. The half-shells are kept in the closed position by latching devices positioned along a meeting line situated in the bottom part (in the 6 o'clock position).
Each half-shell is deployed by means of a jack one end of which is fixed and connected to the turbojet engine, and the other end of which is connected to the shell, at an upper part or in the 12 o'clock position thereof, at a point slightly offset from the hinge axis.
The middle and rear sections are, in the conventional way, joined together by a frame, the first and second half-shells generally being equipped with positioning means which, in the work position, collaborate with complementary positioning means created on the frame.
A nacelle of this type has the disadvantages set out hereinbelow.
When the nacelle is opened, that is to say when the two half-shells are distanced from one another, each half-shell has a tendency to deform. Such deformation is accentuated by the position of the jack and the associated reaction forces. Further, the maintenance operations may be performed out of doors, which means that the presence of wind further accentuates the deformations suffered by the deployed half-shells.
It will be recalled that, in general, the hinge pins are attached to the rear part of the rear section, in the upper region where the half shells meet.
Thus, when the nacelle is in the maintenance position, the ends of the half-shells placed at the lower meeting region, and at the interface between the rear section and the middle section, shift downward and toward the turbojet engine.
These ends, subjected to a great deal of movement may then interfere with the other parts of the nacelle, particularly as a result of the shifting of the ends in the direction of the turbojet engine.
In order to limit such movement of these ends, it is known practice for each half-shell to be equipped with at least one first follower element in the region situated some distance from the hinge axis, the nacelle being fitted with a fixed first guide element, the first follower element being designed to bear against the first guide element as the first half-shell rotates.
In this way, the movement of the region located some distance from the axis of rotation is limited by the follower element bearing against the fixed cam thus limiting the maximum deformation of each half-shell.
However, this type of nacelle entails the use of a guide element that is very long because it has to accompany the movement of the follower element over a significant part of the angular travel of the corresponding half-shell.
The significant size entails structural modifications to other surrounding elements that make up the nacelle.